Electrical pickoff



Dec- 1, 1970 i c. c. BATH 3,544,939

ELECTRI CAL PI CKOFF Filed Jan. 10, 1969 N LL k & Q "S Q q l 9 x, b k L) \x t r l g 09 l 1:23

Q N Q CARL 0. BATH INVENTOR ATTORNEY United States Patent 3,544,939 ELECTRICAL PICKOFF Carl C. Bath, Plantation, Fla., assignor to The Bendix Corporation, a corporation of Delaware Filed Jan. 10, 1969, Ser. No. 792,205 Int. Cl. H0112 21/06 .U.S. Cl. 336-135 2 Claims ABSTRACT OF THE DISCLOSURE An electrical pickotf is described. The inventive pickoif includes a rotatable armature and a symmetrical magnetic circuit. Rotation of the armature causes an imbalance in the reluctance of the magnetic circuit resulting in an output voltage. The magnitude and polarity of the output are indicative of the angular value and direction of the rotation of the armature. A unique configuration of the armature increases the electrical sensitivity of the pickotf, while decreasing the criticality of its initial balancing in a null position.

Many types of electronic control, indicating or measuring systems employ electrical pickolf devices. In many instances the type of system in which the pickolf is employed requires the output of the pickoif to have both an amplitude and a polarity which are indicative of the characteristic under consideration. For this reason, one well known type of pickofl employs a stationary and a rotatable element. The stationary element is a symmetrical magnetic circuit including an input winding and at least one output winding. The rotatable element is situated such that when in a null position the stationary magnetic circuit is in balance and there is no output on the output windings. The movement of the armature due to the function to be measured causes an imbalance in the mag- This output voltage is therefore used as the control or indicating signal. Because this type of device requires a null position the initial balancing is very critical. This criticality makes the pickoff devices very expensive to fabricate and calibrate and therefore is a marked deficiency of the devices. Another deficiency of the devices lies in their insensitivity. Ordinarily such devices yield an output of approximately one volt for each 30 degrees of rotation of the armature from the null position. In many instances the armature is restrained from rotating more than 5 degrees on each side of its null position. The maximum output voltage which can be realized is therefore less than half a volt. Consequently, the systems utilizing the output voltage must be extremely sensitive and relatively noise free. This greatly increases the expense of the control equipment.

It is therefore an object of this invention to provide an electrical pickoif which possesses a high electrical sen sitivity.

It is another object to provide such a device which has a sensitivity of approximately one volt output for each 5 degrees of revolution of the rotatable armature.

It is another object to provide such a device which has an armature which lacks radial symmetry and therefore it is not difiicult to balance in a null position.

It is another object to provide such a device having an armature whcih is configured to increase the magnetic coupling area of the magnetic circuit and thereby increase the electrical sensitivity while decreasing the critically of the initial balancing in a null position.

Further objects, features and advantages of the invention will become apparent from the following description and claims when read in view of the accompanying drawice ings, wherein like numbers indicate like parts and in which:

FIG. 1 is an example of the prior art type device presently existing.

FIG. 2 is a preferred embodiment of the instant invention.

The prior art configuration shown in FIG. 1 includes a stationary portion and rotatable armature. The stationary portion forms a magnetic circuit which includes a Primary Leg 11 and two Secondary Legs 12 and 13. The Primary Leg 11 and Secondary Legs 12 and 13 are connected by a perpendicular Section 14. All the portions 11 through 14 of the stationary section are made of a magnetic permeable material.

A Primary Winding 15 is wound about the Central Post 11 and an alternating input voltage is applied to the Input Terminals 18 and 19. A first Secondary Winding 16 is wound about the Secondary Post 12 and an identical Secondary Winding 17 is wound about the Secondary Post 13. The Secondary Coils 16 and 17 are connected in series with their respective Ends 21 and 22 serving as the output leads of the pickoff device. The Coils 16 and 17 are oppositely wound so that oppositely poled voltages are induced in them. An Armature 23 which is rotatable about an Axis 24 is located between the Secondary Legs 12 and 13. Armature 23 is configured with two Flange Portions 26 and 27 such that there are two degrees of symmetry to the Armature 23. Armature 23 is located with respect to the primary portion of the pickotr, such that there are two Pair Gaps 28 and 29 between Flange 26 and Secondary Legs 12 and 13, respectively.

When the pickolf is initially fabricated, the Armature 23 is located such that there is no output present on Output Leads 21 and 22. This requires the armature to be centered perfectly between the Secondary Legs 12 and 13 in order to balance the two sides of the magnetic circuit. This adjustment is very critical and extremely difiicult to achieve.

In operation the Armature 23 is caused to rotate in some manner. As an example, the Armature 23 could be caused to rotate by the angular movement of a me chanical member of a system so that the output of the pickott device is a function of the angular movement of said member. There are many types of systems in which either the prior art or the inventive pickolf can be used and therefore a further description is not required herein. The rotation of Armature 23, as an example clockwise, causes a decrease in the portion of Flange 2'6 and Secondary Leg 12 which are adjacent to one another. Consequently, the Air Gap 28 increases thereby increasing the reluctance of this portion of the magnetic circuit. The same rotation of Armature 23 has caused an increase of the mating of Flange 26 and Secondary Leg 13. Consequently, Air Gap 29 has decreased by the same amount that Air Gap 28 has increased. This obviously results in a like increase of the reluctance between Flange 26 and Secondary Leg 13. In this condition the overall magnetic circuit has become substantially unbalanced, resulting in a higher voltage being induced in Coil 17 than in Coil 16. The imbalance of voltage across the two coils can then be used to actuate the control or indicating system in which the device is employed. For example, theOutput Terminals 21 and 22 can be connected to a rectifier circuit and then to an indicating meter. Alternatively, the output terminals can be connected to an amplifier and servomotor so that the direction and speed of rotation of the motor is a function of the imbalance of the magnetic circuit.

The inventive embodiment of the pickoff is shown in FIG. 2. In this embodiment the permanently stationed magnetic circuit including Legs 11, 12 and 13 wound with Coils 15, 16 and 17 is identical to the embodiment of FIG. 1. The configuration of Armature 30 is substantially ditferent from the configuration of Armature 23 of the FIG. 1 embodiment. Armature 30 is configured such that its only axis of symmetry is a vertical line, as drawn in FIG. 2. This is different from Armature 23 in that the armature has both a vertical and a horizontal axis of symmetry. Rotation of Armature 30 is about the Axis 24. The top portion of Armature 30 is configured to have two Flat Surfaces 32 and 33 which are respectively adjacent to Secondary Legs 12 and 13. The lengths of Sides 32 and 33 are such that the magnetic coupling between the sides and the Secondary Legs 12 and 13 is substantially increased as compared with that of the FIG. 1 embodiment. Consequently, a change in the width of the Air Gaps 37 and 38 results in a more substantial increase in the reluctance change due to rotation of Armature 30.

Armature 30 is also configured to include a Slot 31 symmetrically positioned around the symmetrical axis of the armature. Slot 31 receives Primary Leg 11 such that there is an Air Gap 36 extending along all sides of the Slot 31. Air Gap 36 is therefore cup-shaped when the sensor is in the null position. Although rotation of Armature 30 causes a change in the width of the Air Gap 36 along the sides of Primary Leg 11, the portion of the air gap between the bottom of the Leg 11 and Slot 31 remains substantially constant for all degrees of rotation. Consequently, the magnetic coupling between Primary Leg 11 and Armature 30 remains virtually unchanged. Slot 31 and the end of Leg 11 are dimensioned such that Armature 30 is free to rotate until one of the Sides 32 and 33 contact either of Secondary Legs 12 and 13. In this position, the imbalance of the magnetic circuit is at a maximum.

The adjustment of Armature 30 into a null position is substantially easier than that of Armature 23. This is so because the intial adjustment requires equal Air Gaps 37 and 38 but the exact vertical location of Axis 24 is of minor importance. This is ditferent from the embodiment of FIG. 1, wherein the initial adjustment requires both angular and a vertical null position. The vertical location is important because the width of the Air Gaps 28 and 29 substantially affects the sensitivity of the sensor. The initial adjustment of Armature 30 is also facilitated by the Heavy Flange 34 which is formed on the bottom portion of the armature. The heavier portion causes the Armature 30 to naturally hang in a vertical position. This is different from the prior art embodiment of FIG. 1 where the Armature 23 has two degrees of symmetry and therefore will balance in any angular position. If balance is required for a particular application, sufficient external mass may be added to the slotted end of Armature 34.

In either of the embodiments, an AC. input must be applied to the Terminals 1'8 and 19. At magnetic balance, equal and opposite alternating voltages are induced in the Secondaries 16 and 17, resulting in cancellation and thus zero output. A change of the angular position of the rotatable armature would then be indicated by the change of amplitude and phase of the output signal.

Although this invention has been described with respect to particular embodiments thereof, it is not to be so limited, as changes and modifications may be made therein which are within the spirit and scope of the invention as defined by the appended claims.

The invention claimed is: 1. In an electrical pic'kofi' having a stationary element including one leg wound with a first coil and other legs symmetrically positioned about said one leg wound with other coils, and

a rotatable armature symmetrically positioned with respect to said other legs in a null position and asymmetrically positioned with respect to said other legs in an output position,

the improvement which comprises:

said armature having only one axis of symmetry said axis of symmetry being perpendicular to the axis of rotation, substantially parallel sides forming air gaps between said sides and said other legs, the lengths of said air gaps being substantially equal when said armature is in said null position and unequal when said armature is in said output position,

said armature also including a hollowed notched portion receiving the end of said one leg, said hollowed portion and said end forming a cupshaped air gap, the sides of said cup-shaped air gap being wider than the air gaps between said armature and said other legs.

2. An electrical pickoff as recited in claim 1 wherein said armature includes a flux changing portion and a positioning portion arranged diametrically opposed about the axis of rotation of said armature;

said positioning portion having a mass greater than that of said flux changing portion so that said armature readily assumes a symmetrical position with respect to said stationary element.

References Cited UNITED STATES PATENTS 3,152,311 10/1964 Bojanski 366-133X FOREIGN PATENTS Ad. 14,591 11/1911 France 336- 777,638 12/1934 France 336-134 THOMAS J. KOZMA, Primary Examiner 

